An engine may include an external exhaust gas recirculation (EGR) system to reduce NOx emissions and increase engine efficiency. The external EGR system may couple an engine exhaust manifold to an engine intake manifold via an EGR passage. Further, the EGR system may include temperature and/or pressure sensors to estimate the amount of EGR flowing to engine cylinders. During the course of operation, an EGR actuator, sensor, conduit, or hose may become disconnected. The EGR system component may become dislodged due to engine boost pressure, vibrations caused by irregular road surfaces, or other conditions. Degradation of the EGR system may degrade engine performance, for example, by increasing emissions or reducing fuel economy.
As one example, an EGR flow rate may be determined based on output of a differential pressure sensor, such as a delta pressure feedback of EGR (DPFE) sensor. Typically, the differential pressure sensor includes an upstream hose and a downstream hose, which are both coupled to the EGR passage on either side of a metered orifice. When EGR flows through the EGR passage, a pressure drop occurs across the metered orifice, which is measured by the differential pressure sensor and used to determine the EGR flow rate. If the upstream hose becomes disconnected, the differential pressure sensor may measure a large pressure differential (e.g., delta pressure), indicating a high EGR flow rate, even if no EGR is flowing. This may degrade air-fuel control, increase emissions, and lead to engine knock, for example.
Various approaches are provided for periodically or opportunistically monitoring EGR system components. One example approach for diagnosing an EGR differential pressure sensor is shown by Cullen et al. in U.S. Pat. No. 5,190,017. Therein, a measured EGR flow is compared to an expected EGR flow based on measurements from redundant sensors to determine whether one of the EGR system components has become inoperable. If the two estimates deviate by a calibrated amount for a sustained period of time, then a fault condition in the EGR system is indicated. Specifically, disconnection of the upstream hose may be indicated based on a delta pressure measured by the EGR differential pressure sensor being greater than an expected deviation from an exhaust backpressure.
However, the inventors herein have recognized potential issues with such systems. As one example, redundant sensors and methods for determining EGR flow may add to vehicle complexity and costs. Additionally, if the upstream hose of the EGR differential pressure sensor becomes disconnected after the upstream hose test is performed, the disconnection may not be identified in a timely fashion, which may degrade engine operation, increase emissions, and reduce the life of engine components.
The inventors herein have recognized that EGR system degradation due to a disconnected EGR differential pressure sensor upstream hose may result in a specific combination of changes to measurable engine parameters, which may be used to identify the EGR system degradation. In particular, if the upstream hose is disconnected, there is actually no EGR, which causes engine knocking to increase. As a result of the increased knock, adaptive spark may be retarded, such as toward a maximum retard clip, even though the EGR sensor continues to indicate that there is a high EGR flow rate (a condition when knock is not expected). Additionally, since there is no EGR actually displacing air in the induction system, a lower air flow is measured, and the engine controller may fuel the engine in accordance with the lower air flow. As a result, a measured exhaust air-fuel ratio may run leaner than expected. By monitoring for the above-mentioned change in engine parameters (or a combination thereof), degradation of an EGR differential pressure sensor due to a disconnected upstream hose can be opportunistically diagnosed using existing engine components.
In one example, EGR system degradation may be diagnosed by a method comprising: during engine operation with a commanded amount of EGR, responsive to at least one of an integrated knock intensity of an engine being greater than a threshold intensity and a fuel control correction of fuel supplied to the engine being greater than a threshold enrichment, setting an exhaust gas recirculation (EGR) rate to zero. Further, EGR system degradation may be indicated, and an active EGR differential pressure sensor upstream hose diagnostic test may be performed to confirm the diagnosis.
As one example, during engine operation with EGR commanded, an engine controller may non-intrusively monitor one or more engine parameters to diagnose for EGR differential pressure sensor upstream hose disconnection. For example, the controller may monitor engine knock intensity and frequency over a number of engine cycles. If the integrated intensity exceeds a threshold, a criterion for potential disconnection of the hose may be considered satisfied. As another example, adaptive spark may be monitored and if spark hits a retard clip within a defined number of engine cycles, another criterion for potential disconnection of the hose may be considered satisfied. As a further example, feedback fuel control may be monitored, and if fuel has to be enrichened by more than a threshold to maintain a target air-fuel ratio (e.g., to maintain a stoichiometric air-fuel ratio based on feedback from an air-fuel ratio sensor), then a further criterion may be considered met. If one or more or all of the criteria are met, the controller may infer that the upstream hose coupled to the EGR system differential pressure sensor is disconnected. Responsive to the indication of degradation, further EGR flow may be disabled by setting the EGR rate to zero, while spark and fuel are adjusted based on a zero EGR flow rate, independent of the output of the EGR sensor. For example, the spark timing may be retarded relative to when a non-zero amount of EGR is supplied, and the fueling amount may be increased in order to account for a greater cylinder air amount compared to when EGR is supplied. In addition, an intrusive EGR differential pressure sensor monitor may be run at the earliest to confirm the indication of degradation.
In this way, EGR system degradation may be diagnosed using existing engine sensors, without compromising the accuracy of diagnosis. The technical effect of monitoring for a specific combination of changes in engine knock intensity, spark control, and fuel control during engine operation with commanded EGR is that EGR hose disconnection can be reliably identified anytime it occurs during engine operation, including after a dedicated upstream hose monitor has run. By commanding the hose monitor to be run in response to degradation being detected during engine operation, disconnection may be confirmed and addressed in a timely fashion. By disabling EGR and setting spark timing and fueling for zero EGR responsive to the degradation, a further occurrence of knock may be reduced, thereby improving fuel economy and extending the life of engine components. In addition, exhaust emissions quality may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.